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From fe512f6331aa2cda166c08988965010dd06d68e3 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 19 Sep 2012 14:50:37 +0200
Subject: [PATCH 206/347] printk: Make rt aware
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz
Drop the lock before calling the console driver and do not disable
interrupts while printing to a serial console.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/printk/printk.c | 33 ++++++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7b774743e1ac..c06b1e00448d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1654,6 +1654,7 @@ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
return do_syslog(type, buf, len, SYSLOG_FROM_READER);
}
+#ifndef CONFIG_PREEMPT_RT_FULL
/*
* Special console_lock variants that help to reduce the risk of soft-lockups.
* They allow to pass console_lock to another printk() call using a busy wait.
@@ -1794,6 +1795,15 @@ static int console_trylock_spinning(void)
return 1;
}
+#else
+
+static int console_trylock_spinning(void)
+{
+ return console_trylock();
+}
+
+#endif
+
/*
* Call the console drivers, asking them to write out
* log_buf[start] to log_buf[end - 1].
@@ -1809,6 +1819,7 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
if (!console_drivers)
return;
+ migrate_disable();
for_each_console(con) {
if (exclusive_console && con != exclusive_console)
continue;
@@ -1824,6 +1835,7 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
else
con->write(con, text, len);
}
+ migrate_enable();
}
int printk_delay_msec __read_mostly;
@@ -2018,20 +2030,30 @@ asmlinkage int vprintk_emit(int facility, int level,
/* If called from the scheduler, we can not call up(). */
if (!in_sched && pending_output) {
+ int may_trylock = 1;
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+ /*
+ * we can't take a sleeping lock with IRQs or preeption disabled
+ * so we can't print in these contexts
+ */
+ if (!(preempt_count() == 0 && !irqs_disabled()))
+ may_trylock = 0;
+#endif
/*
* Disable preemption to avoid being preempted while holding
* console_sem which would prevent anyone from printing to
* console
*/
- preempt_disable();
+ migrate_disable();
/*
* Try to acquire and then immediately release the console
* semaphore. The release will print out buffers and wake up
* /dev/kmsg and syslog() users.
*/
- if (console_trylock_spinning())
+ if (may_trylock && console_trylock_spinning())
console_unlock();
- preempt_enable();
+ migrate_enable();
}
if (pending_output)
@@ -2503,6 +2525,10 @@ void console_unlock(void)
console_seq++;
raw_spin_unlock(&logbuf_lock);
+#ifdef CONFIG_PREEMPT_RT_FULL
+ printk_safe_exit_irqrestore(flags);
+ call_console_drivers(ext_text, ext_len, text, len);
+#else
/*
* While actively printing out messages, if another printk()
* were to occur on another CPU, it may wait for this one to
@@ -2521,6 +2547,7 @@ void console_unlock(void)
}
printk_safe_exit_irqrestore(flags);
+#endif
if (do_cond_resched)
cond_resched();
--
2.36.1
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